I think we all agree to some degree or another that the term Pre-Bonsai applies to material that has had some work done on it with bonsai culture in mind, being initial root work/reduction to some branch removal. This does not necessarily mean that the definition Pre-Bonsai needs to mean almost ready for prime time but it does not rule that definition out either.
To give you an idea what I mean. In market places where Trident Maples are available and cultivated for bonsai it is possible to obtain this tree in a form that is nothing more than a cut down trunk at first glance. But upon closer observation the tree has been cut down from a larger tree, the top regrown and cut down again numerous times to develop a tapered trunk. These trees usually have a good deal of consistent root prunings. At this point they may not look like a bonsai ready for the final pot but they most certainly are Pre-Bonsai. The configuration of the trunk is something you are not likely to find naturally or from a nursery.
As to the Juniper referenced in the earlier post, It is most likely a pre-bonsai and has most likely had some human intervention done on it prior to this photograph. At this point it is a pre-bonsai but the question is was it a pre-bonsai before this. I have run across a few nursery trees that looked a step away from being a bonsai with a little wire, pruning and placing in a pot if the roots will allow that much reduction. This is rare but it is possible. I have also noticed Yamidori in the fields that were near the same point. Are they pre-bonsai? Yes and no. The key issue is harvesting and survival.
